XenForo developer

Given that you've moved to a forums sub-directory, you likely can't redirect the "forums" links using that code. There will certainly be some ambiguity there. But what happens if you remove that from the the 2 regexes? What problems are you running into?

XenForo developer

I'd guess that may be related to another option that's displayed on that page. Unfortunately, the error won't give you the specific value and this is generally something that'd be more of a developer error message. You may need to disable add-ons to see if it gets resolved (though I'm not positive it will actually hide options from disabled add-ons; there would be pluses and minuses to that).